1. Field of the Invention
The present invention relates to a thin-film transistor array used in a liquid crystal display (LCD) device, in which display electrodes connected to thin-film transistors are arranged in a matrix, and an LCD apparatus using the thin-film transistor array.
2. Description of the Related Art
There has conventionally been known an active matrix type liquid crystal display device using a thin film transistor array (hereinafter referred to as "TFT-LCD") in which thin film transistors ("TFT") and pixel electrodes are arranged in a matrix.
An example of such a conventional TFT-LCD is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 59-166984. FIG. 32 shows an equivalent circuit of the TFT array used in this TFT-LCD.
As is shown in FIG. 32, in the TFT array, address lines 2 and data lines 3 are arranged in rows and columns on a transparent insulating substrate 1 such that the address lines 2 intersect the data lines 3 at right angles. TFTs 4 having their gates connected to the address lines 2 and their drains connected to the data lines 3 are arranged in a matrix at the intersections of the address lines 2 and data lines 3. Pixel electrodes 5 connected to the sources of the TFTs 4 are arranged in a matrix. A short-wiring or short-ring 6 is formed on an outer peripheral portion of the transparent insulating substrate 1 along the outer periphery of the substrate 1. The data lines and address lines 3 electrically are connected to the short-wiring 6 via their terminal portions 2a and 3a.
After the processing of the TFT array is completed, the substrate 1 is cut along broken lines 7 shown in FIG. 32. Then, the substrate 1 is bonded to an opposed substrate having opposed electrodes with a predetermined gap therebetween, and a liquid crystal material is sealed between these substrates. Thus, an LCD device is formed.
In the manufacturing process of this TFT array, a DC static electricity occurs while the substrate is exposed to a plasma or subjected to a rubbing process. However, since all address lines 2 and data lines 3 are connected to the short-wiring 6, the potential of all address lines 2 and data lines 3 is equalized and it is possible to prevent a problem of dielectric breakdown or short-circuit due to a discharge of static electricity between electrodes.
However, in the manufacturing process of the conventional LCD device using the TFT array, the TFT array is bonded to an opposed substrate via a sealing member and then the short-wiring 6 is cut along broken lines 7 and removed. Thus, owing to static electricity occurring in the subsequent manufacturing steps of adhering a polarizing plate, connecting a driving circuit, etc., there may occur dielectric breakdown, line breakage, a characteristic variation of the TFTs, etc., resulting in a display defect in the LCD device. Consequently, a manufacturing yield may deteriorate.
FIG. 33 shows a structure for preventing dielectric breakdown, etc. due to static electricity in the LCD device after the TFT array is completed. A short-wiring 8 is formed between a display region, in which the pixel electrodes 5 connected to the TFTs 4 are arranged in a matrix, and a terminal array section in which the terminal portions 3a of data lines 3 and the terminal portions 2a of address lines 2 are arranged, such that the short-wiring 8 surrounds the display region. The short-wiring 8 is connected to the data lines 3 and address lines 2 by protection elements 9 each comprising a plurality of diodes designed to have non-linear current-voltage characteristics, as shown in FIG. 34.
In the TFT array having the protection elements 9, the protection elements 9 are turned on if static electricity occurs after the short-wiring 6 shown in FIG. 32 is cut and a high voltage is applied between the short-wiring 6 and the data lines 3 and address lines 2. As a result, a voltage difference between the data lines 3 and address lines 2 is eliminated, and dielectric breakdown between the data lines 3 and address lines 2 can be prevented.
The structure of the above-described protection elements, however, is complex, and steps other than those for forming TFTs are required. Thus, the number of steps for manufacturing the TFT panel increases and the manufacturing yield of TFTs considerably deteriorates owing to the increased steps.
The conventional TFT panels shown in FIGS. 32 and 33 have a problem in that the TFT panel has a low electrostatic destruction preventing effect against pulsatile static electricity, which is applied when the TFT panel is handled by operators, when the TFT panel is put in contact with an electrified manufacturing apparatus, when the rubbing roller approaches the substrate, or when the substrate is cut, at which time most of electrostatic destruction occurs.
Furthermore, in the TFT panel having the protection elements shown in FIG. 32, a leak current flows between the address lines 2 and data lines 3 via the protection elements 9. Thus, much crosstalk occurs, the display quality deteriorates and much current is consumed.